1. Field of the Invention
This invention relates to improvements in a fuel vapor treatment device or vapor storage canister for temporarily storing fuel vapor to prevent evaporative emission in a vehicle.
2. Description of the Prior Art
An evaporative emission control system of an automotive vehicle generally includes a device or vapor storage canister that treats fuel vapor from a fuel tank and/or carburetor. The fuel vapor treatment device is provided at its one end with an inlet pipe connecting to a fuel tank so that fuel vapor is charged to the device, and an outlet pipe connecting to an air intake pipe forming part of the intake system of an engine so that the fuel vapor within the device is purged. The fuel vapor treatment device is provided at the other end thereof with an air pipe through which atmospheric air can be sucked into the device. A fuel vapor absorbent such as activated carbon, activated clay, silica gel is filled within the casing of the device. When the vehicle is in standstill or during fuel supply, fuel vapor in the fuel tank is introduced into the casing to be absorbed in the fuel vapor absorbent. The thus absorbed fuel vapor is purged from the fuel vapor absorbent with atmospheric air sucked into the casing under the vacuum in the intake system air intake pipe upon engine running, in which the purged fuel vapor is fed to the side of the air intake pipe.
It is a matter of general knowledge that the fuel vapor treatment device exhibits a high vapor absorbing performance (under the action of the fuel vapor absorbent) in case that the canister has a large length relative to a cross-sectional area. However, if the treatment device is considerably large in apparent length, it is inconvenient to use in cases where it is disposed in a narrow space or an engine room. In view of this, it has been proposed to improve the vapor absorbing performance without increasing the apparent length of the treatment device, as disclosed in Japanese Patent Provisional Publication No. 1-159455.
Such a fuel vapor treatment device is shown in FIGS. 6 and 7 and includes a casing 1 formed of a plastic and generally pipe-shaped. The inside space of the casing 1 is separated into two chambers 4a, 4b by a partition plate 4 integral with an end wall 2 of the casing 1 and has a length slightly smaller than the longitudinal dimension of the inside space of the casing 1. The end wall 2 is provided at its part closing the chamber 4a with an inlet pipe 2a and an outlet pipe 2b, and at its part closing the chamber 4b with an air pipe 2c. Additionally, a perforated support plate 6a and a filter member 6b are disposed inside the casing 1 and located at both the opposite end sections of the casing inside space in a manner to maintain a space between them and the end wall 2 or a cover plate 3 covering the open end of the casing 1. A fuel vapor absorbent 5 is filled under pressure in a space between the opposite filter members 6b, 6b. With this arrangement, when the fuel vapor from the fuel tank is charged to the treatment device, the amount of fuel vapor passing through the fuel vapor absorbent 5 is increased per unit area since the cross-sectional area of the treatment device is decreased by the partition plate 4. Additionally, the fuel vapor can be effectively absorbed in the fuel vapor absorbent 5 upon being passed through the two chambers 4a, 4b, which are contiguous in the U-shape.
However, drawbacks have been encountered in the above discussed conventional fuel vapor treatment device, as set forth below. That is to say, it will be understood that there is the necessity to partly form a depression on the surface of the casing 1 at a part near the cover plate 3 to avoid an interference of the treatment device with an obstacle D such as another apparatus or the like as shown in FIG. 7. In this case, it is impossible to fabricate a one-piece integral body of the casing 1 and the end wall 2 from view points of problems concerning fabrication and filling of the fuel vapor absorbent 5. More specifically, the one-piece integral body (a product) and a core used for fabrication cannot be drawn from a metallic mold after completion of the fabrication or plastic molding. Additionally, when the fuel vapor absorbent 5 is filled into the casing 1, a hollow space (not supplied with the absorbent) is unavoidably formed near the step-wise portion of the inner wall of the casing 1.
Accordingly, it is required to form or fabricate the casing 1 and the end wall 2 as two separate members as shown in FIG. 8, in which the end wall 2 is connected to the end face of the casing 1 under a frictional welding, after the fuel vapor absorbent 5, the support plate 6a and the like are supplied inside the casing 1. In this case, it is easy to connect the end wall 2 (as a separate member) to the end face of the casing 1 and to the end face of the partition plate 4. Additionally, it is also relatively easy to confirm a gas-tight seal under the connection of the end wall 2 with the casing 1. However, it is difficult to confirm a gas-tight seal under the connection of the end wall 2 with the partition plate 4.
The reason therefor will be discussed. The confirmation of the gas-tight seal can be accomplished by sinking the whole fuel vapor treatment device in water upon providing blind covers respectively to the outlet pipe 2b and the air pipe 2c and supplying suitable air through the inlet pipe 2a into the casing 1 followed by providing a blind cover to the inlet pipe 2a. If the end wall 2 is fully sealingly connected to the casing 1, no water bubble is produced. If there is a failure in gas-tight seal between the end wall 2 and the casing 1, water bubbles are produced thereby confirming a failed gas-tight seal.
However, concerning confirmation of the gas-tight seal between the partition plate 4 and the end wall 2, a connecting portion of the partition plate 4 and the end wall 2 is not exposed to the outside so as not to contact with water, and therefore leaking air merely stays within the casing even though air leak arises at the connection portion. As a result, the leaking air cannot escape into water thus never producing water bubbles. Thus, it is impossible to confirm as to whether the gas-tight seal is complete or not between the partition plate 4 and the end wall 2, thus resulting in producing inferior goods of the fuel vapor treatment device.